之间的区别<queue>的就位和推动

Question

What are the differences between <queue> 's emplace and push?

here's explanation about the std::queue::emplace and std::queue::push .

Both methods add element after its current last element, return None .

Answer 1

push() adds a copy of an already constructed object into the queue as a parameter, it takes an object of the queue's element type.

emplace() constructs a new object in-place at the end of the queue. It takes as parameters the parameters that the queue's element types constructor takes.

If your usage pattern is one where you create a new object and add it to the container, you shortcut a few steps (creation of a temporary object and copying it) by using emplace() .

Example

#include <iostream>
#include <stack>
using namespace std;

struct Point_3D
{
    int x, y, z;
    Point_3D(int x = 0, int y = 0, int z = 0)
    {
        this->x = x, this->y = y, this->z = z;
    }
};


int main()
{
    stack<Point_3D> multiverse;

    // First, Object of that(multiverse) class has to be created, then it's added to the stack/queue
    Point_3D pt {32, -2452};
    multiverse.push(pt);

    // Here, no need to create object, emplace will do the honors
    multiverse.emplace(32, -2452);

    multiverse.emplace(455, -3);
    multiverse.emplace(129, 4, -67);
}